The subject matter of the present invention is the recovery of nickel values from a low-grade complex nickel ore. The extraction process comprises a simultaneous grind-leach of the ore.
Commercially significant nickel deposits are of two main types: (i) sulphides which are primary nickel ores or rock materials and (ii) laterites and garnierites which are secondary nickel ores or rock materials. The nickel bearing laterites and garnierites result from the deterioration of primary rock materials through weathering, erosion and related chemical and physical processes during which the nickel values are greatly concentrated compared with the primary rock materials and are deposited in layers of altered residual rock materials. These nickel bearing laterites and garnierites normally contain from about 1.5 to about 3 percent nickel.
Primary rock materials with a low nickel content, typically below 0.5 percent, are found in various Precambrian and Cordillera regions in Alaska, Asia, Australia, Canada, Northern Europe and in various tropical and subtropical regions. In Canada the low-grade primary nickel ores are characteristically found in the form of peridotite or other ultramafic rock formations. These formations represent huge reserves of nickel. However, due to the small amounts of nickel present it is difficult to extract nickel from these ores with any degree of commercial feasibility. Several techniques have been used in attempting to extract the nickel on a commercially feasible basis. These methods include various flotation, magnetic separation and roast-leach processes. However, these techniques have not proved to be entirely satisfactory, either because of rather low nickel recoveries or because of rather high costs.
We have discovered a novel process for extracting nickel from nickel bearing sulfide ores of the above type. This process gives high nickel recoveries and offers promise of low cost. The process utilizes simultaneous grinding and leaching of these ores with an aqueous ammoniacal solution.